1. Field of the Invention
This invention relates to a heat-insulating engine structure and method of manufacturing the same in a ceramic engine and the like.
2. Description of the Prior Art
An engine member for heat-insulating engine and the like with a ceramic material utilized for heat insulating or resisting is disclosed hitherto, for example, in Japanese Patent Laid-Open No. 90955/1985. A heat-insulating engine structure disclosed in the publication will be described in outline with reference to FIG. 7. In FIG. 7, a heat-insulating engine structure is indicated generally by a reference numeral 30. The heat-insulating engine structure 30 comprises forming a surface of thermal reflection on an inner circumferential wall 33 of a cylindrical part 32 provided on lower half portion of a cylinder head 31, fitting a ceramic head liner 34 shaped like an inverted cup in the cylindrical part 32 of the cylinder head 31 with a void 35 left around. Then, a heat insulating material 36 such as ceramics fiber, glass fiber or the like is placed in the void 35 between the cylindrical part of the cylinder head 31 and the head liner 34. Further, an upper end wall of the head liner 34 is pushed to the inner end wall 33 of the cylindrical part 32 of the cylinder head 31 through a gasket 43, a lower end wall 42 of the head liner 34 is also pushed to upper end portions of a cylinder block 37 and a cylinder liner 39 through an elastic gasket 44, thus a stress concentration to be applied to the head liner 34 due to unbalance of tightening force and thermal deformation is relieved, and the void 35 is formed, therefore a heat conduction from the head liner 34 surrounding a combustion chamber 40 to a cylinder head 31 is cut off, and a heat dissipation can be suppressed. Further, a heat radiation is reflected on the surface of thermal reflection of the inner end wall 33, thus suppressing a heat conduction to the cylinder head 31. Furthermore, by placing a heat insulating material 36 such as ceramics fiber or the like and annular seal members 45, 46 in the void 35, an air convection in the void 35 is prevented, and a heat transfer from a wall portion of the head liner 34 to the cylinder head 31 can be suppressed. Accordingly, a heat of the combustion chamber 40 can be suppressed from being dissipated externally through the head liner 34, therefore hot exhaust gas can be sent to an exhaust turbo super-charger and others by way of the exhaust passage, thereby utilizing a thermal energy of the exhaust gas maximumly.
However, it is very difficult to secure a heat insulation characteristic thoroughly in the heat-insulating engine member such as cylinder head or the like with a ceramic material utilized for heat insulating or resisting as mentioned, and thus what is problematic is that a wall of the head liner 34 must be thickened inevitably so as to ensure a satisfactory heat insulation characteristic. That is, the portion facing the combustion chamber of an engine is constituted of ceramics such as silicon nitride or the like surpassing in heat resistance, heat insulating efficiency and heat shock resistance, to withstand a high-temperature combustion gas. However, if a wall of the head liner constituting the combustion chamber is too thick, then a thermal capacity becomes excessively large, and a deterioration of suction efficiency may result. Thus, problems remain as to how to construct the head liner for better suction efficiency and cycle efficiency while thinning a wall of the head liner constituting the combustion chamber in construction, minimizing a thermal capacity, and securing strength and pressure resistance of the head liner.